Use of wax-like compounds in photo toner

ABSTRACT

Photo toners including a wax-like compound of the formula (I), detailed in the specification. In formula (I), R 1  represents the group —CH 2 —O—CO—R 3  or CH(OH)—CH 2 —O—CO—R 3 , R 2  represents an alkyl radical comprising between 1 and 4 C atoms or halogen, R 3  represents an unbranched alkyl radical comprising between 16 and 36 C atoms, m is 1, 2 or 3, and n is between 0 and (6−m).

The present invention relates to the use of wax-like compoundscontaining aromatic units in photo toners and also photo tonerscomprising such compounds.

Photo toners comprising resins, pigments, charge control agents andwaxes and also, if desired, flow improvers are customarily used inmodern copying processes. In the copying procedure, the pulverulentphoto toners usually firstly form an image of the item to be copied on atransfer roller and are from there transferred to the copying paper andsubsequently subjected to thermal fixing.

The waxes present as formulation component in the toner act as releaseand anti-offset agents to aid detachment of the photo toner from thefixing roller, act as coupling agents in transfer to the paper and, inthe preparation of the toner, act as dispersants and thus contribute tohomogeneous distribution of the pigments.

The demand for ever faster copiers requires correspondinglyquick-responding toner systems and places severe demands on theindividual components of the toner formulation.

As wax components in photo toners, use has hitherto been madepredominantly of hydrocarbon waxes such as polyethylene or polypropylenewaxes. These waxes do not meet the requirements of modern fast-runningcopying machines in all aspects. In particular, there is a need for waxcomponents having improved anti-offset action, an improved action inrespect of adhesion of the printing to the paper and further-optimizedpigment-dispersing properties.

EP 0 291 872 A1 describes wax-like esters of aromatic alcohols and theiruse as lubricants for highly transparent thermoplastic polymers.

It has now surprisingly been found that such polar, wax-like compoundscontaining aromatic groups are particularly useful as additives forphoto toners. In particular, such waxes achieve homogeneous dispersionof the pigment in the production of the toner and an improvedanti-offset action and increased adhesion of the printing to the paperin the fixing process.

The invention accordingly provides for the use of wax-like compounds ofthe formula (I)

in photo toners,

-   where R¹ is the group-   —CH₂—O—CO—R³ or —CH(OH)—CH₂—O—CO—R³,-   R² is an alkyl radical having from 1 to 4 carbon atoms or halogen,-   R³ is an unbranched alkyl radical having from 16 to 36 carbon atoms    and-   m is 1, 2 or 3 and n is from 0 to (6−m).

In the formula (I), preference is given to R being the group

-   —CH₂—O—CO—R³,-   R² being an alkyl radical having from 1 to 4 carbon atoms or    halogen,-   R³ being an unbranched alkyl radical having from 16 to 36 carbon    atoms and-   m being 1, 2 or 3 and n being from 0 to (6−m).

The invention further provides photo toners comprising at least onepigment component, a resin component and a wax-like component of theformula (I) containing aromatic units.

The wax-like compounds of the formula (I) which can be used according tothe invention are formed by reacting aromatic compounds of the formula(II)

or the formula (III)

with the carboxylic acids of the formula (IV)R³—COOH  (IV).

In these formulae,

-   R¹ is the group-   —CH₂—O—CO—R³ or —CH(OH)—CH₂—O—CO—R³,-   R² is an alky radical having from 1 to 4 carbon atoms or halogen,    preferably an alkyl radical having from 1 to 2 carbon atoms or    chlorine,-   R³ is an unbranched alkyl radical having from 16 to 36 carbon atoms,    preferably from 26 to 32 carbon atoms,-   R⁴ is the group —CH₂OH or —CH(OH)—CH₂—OH, preferably —CH₂OH,-   R⁵ is the group

and

-   m is 1, 2 or 3, preferably 1 or 2, and-   n is from 0 to (6−m), preferably from 0 to 3.

Suitable starting compounds of the formula (II) are, for example, benzylalcohol, o-, m-, p-tolyl carbinol, chlorobenzyl alcohol, bromobenzylalcohol, 2,4-dimethylbenzyl alcohol, 3,5-dimethylbenzyl alcohol,3,4,5-trimethylbenzyl alcohol, p-cumine alcohol, 1,2-phthalyl alcohol,1,3-bis(hydroxymethyl)benzene, 1,4-bis(hydroxymethyl)benzene.

An example of a suitable starting compound of the formula (III) isstyrene oxide.

Suitable carboxylic acids of the formula (IV) are, for example,arachidic acid, behenic acid, tetracosanoic acid, cerotic acid, montanicacid, melissic acid, in particular technical-grade montanic acid whichis essentially a mixture of C₁₈-C₃₆-carboxylic acids with a predominantproportion of C₂₆-C₃₂-carboxylic acids and is obtained by oxidativebleaching of crude montan wax (cf., for example, Ullmann's Encyclopediaof Industrial Chemistry, 5th edition, 1996, vol. A 28, pp. 122-150).

Methods of preparing the compounds which can be used according to theinvention are reported in EP-0 291 872 A1.

Photo toners generally comprise resins based on polyesters orstyrene-acrylate copolymers as base components. As charge controlagents, which aid the transport of the toner from the photo roller ontothe paper substrate, use is made of, for example, quaternary ammoniumsalts for a positive charge and, for example, aluminum-azo complexes fora negative charge of the toner powder. To aid powder flow, small amountsof finely divided silicas can be added to the toner powder.

Depending on the desired color, suitable black or colored pigments areadded in the thermoplastic mixture of the toners.

EXAMPLES

The acid numbers reported below were determined in accordance with DIN53402, and the dropping points were determined in accordance with DIN51801/2.

Example 1

90 parts by weight of styrene-acrylate resin (type CPR 100, manufacturedby Mitsui; glass transition temperature 60° C.; MFR/140° C. 5 g/10 min)were homogeneously mixed with 4 parts by weight of a black pigment(carbon black having a particle size of 2 μm; manufacturer: Timcal), 1.0parts by weight of a charge control agent (Copy Charge N4S,manufacturer: Clariant GmbH) and 4 parts by weight of a reaction productused according to the invention of technical-grade montanic acid andbenzyl alcohol having an acid number of 25 and a dropping point of 77°C. at 150° C. in a kneader. This mixture was then comminuted to give atoner powder having a mean particle size of 12 μm (100%<20 μm). 0.5parts by weight of a silica-based flow improver (type HDK, manufacturer:Wacker) were then added to the toner powder. 5 g of this nowfree-flowing mixture were mixed with 95 g of iron powder and placed inthe reservoir of a copier.

Toner powder was applied in an area of 20×100 mm to a sheet of paper bymeans of the photomagnetic roller in the copier. This image was thenfixed by means of a roller assembly comprising a rigid heatable rollerand an elastic cold roller, at 160° C. and a linear speed of 150 mm/s. Afurther white sheet of paper was subsequently passed through the hotpair of rollers and was examined for toner residues. No “ghost pictures”could be seen on the white sheet of paper.

Example 2

1 g of the toner powder from example 1 was stirred with 2 g of ethanoland applied by means of a doctor blade to a paper substrate (layerthickness: 40 μm). After the solvent had been dried off at 40° C., theremaining powder layer was fixed at 140° C. and a linear velocity of 120mm/s. The fixed toner layer was examined by means of a Prufbanrubbing-off test as is used in the testing of printing inks. Nomeasurable abraded material was found when the paper was rubbed againsttoner for 50 strokes. When the toner layer was folded through 180°, novisible fold lines and flaking were found.

Example 3

The procedure of example 1 was repeated, but a reaction product whichcan be used according to the invention of technical-grade montanic acidand styrene oxide (acid number 18 mg KOH/g, dropping point 76° C.) wasused in place of the benzyl montanate wax used in example 1. At the sametime, the proportion of pigment was reduced by 25%. Otherwise, theprocedure was as in example 1. The printed images displayed the samedepth of shade as a standard without wax tested in parallel in themanner described in example 1. This indicates that the addition of waxachieves more effective pigment dispersion.

1. A photo toner comprising at least one pigment component, a resin component and a wax-like compound of the formula (I):

where R¹ is the group —CH₂—O—CO—R³ or —CH(OH)—CH₂—O—CO—R³, R² is an alkyl radical having from 1 to 4 carbon atoms or halogen, R³ is an unbranched alkyl radical having from 16 to 36 carbon atoms and m is 1, 2 or 3 and n is from 0 to (6−m).
 2. The photo toner as claimed in claim 1, wherein R¹ is the group —CH₂ _(—O—CO—R) ³, R² is an alkyl radical having from 1 to 4 carbon atoms or halogen, R³ is an unbranched alkyl radical having from 16 to 36 carbon atoms and m is 1, 2 or 3 and n is from 0 to (6−m).
 3. A photo toner comprising at least one pigment component, a resin component and wax-like compounds of the formula (I):

where R¹ is the group —CH₂—O—CO—R³ or —CH(OH)—CH₂—O—CO—R³, R² is an alkyl radical having from 1 to 4 carbon atoms or halogen, R³ is an unbranched alkyl radical having from 16 to 36 carbon atoms and m is 1, 2 or 3 and n is from 0 to (6−m).
 4. The photo toner as claimed in claim 3, wherein R¹ is the group —CH₂—O—CO—R³, R² is an alkyl radical having from 1 to 4 carbon atoms or halogen, R³ is an unbranched alkyl radical having from 16 to 36 carbon atoms and m is 1, 2 or 3 and n is from 0 to (6−m). 